This invention relates generally to seat adjusters and more specifically to powered seat adjusters which allow a seat to be adjusted to a desired elevation and pitch.
It is known in the art to provide power seat adjusters for a vehicle seat where the forward end elevation or the rearward end elevation of the seat may be set independently. An example of a typical seat adjuster is shown in U.S. Pat. No. 4,664,351 issued to Hans Borlinghaus on May 12, 1987.
The Borlinghaus patent discloses a seat adjuster assembly that has two adjusters, each of which has a floor plate, sometimes referred to as an upper channel, slidably carried on a lower channel for forward and rearward movement within the vehicle. The adjuster also has a top plate which is generally parallel with the floor plate. To add support, the top plate and floor plate are connected by a rigid link pivotally connected to the top plate and floor plate along opposite ends of the rigid link. Also provided at the forward end and rearward end of the floor plate are a forward lift assembly and a rearward lift assembly, respectively, to allow adjustment of the seat elevation and pitch. The forward lift assembly and the rearward lift assembly each include a nonrotating jack screw which is raised and lowered by a powered gearing system. The forward lift assembly and the rearward lift assembly also each have a lift plate, or lift bracket, fixably connected to the top of each of the respective jack screws. The lift plate is a substantially thin elongated member which fits into a thin elongated fore and aft slot of the top plate. The lift plate is retained on the top plate by a nut and washer combination. To adjust the seat, the forward lift assembly or the rearward lift assembly is selectively raised or lowered. The connecting rigid link, which has a fixed rotational axis with the top plate and the floor plate, pivots with a fixed arc. Therefore, either the lift assembly connection to the top plate or the rigid link must provide for sliding movement as well as pivotal motion.
The Borlinghaus patent is directed to an operational problem experienced by many seat adjusters wherein, at the end of travel in the upward or downward direction, the jack screw will be urged to rotate slightly even though it is retained by the overlap of the top plate with the lift plate. This overlap of the top plate and the lift plate will have a slight clearance and the lift plate at the end of the travel of the jack screw will be slightly rotated into an interference position with the top plate. This interference will cause intermittent freezing of the parts thereby giving the seat an uneven and jerking vertical motion. Although the intermittent freezing and jerking free motion is not critical in the functional operation of the seat adjuster, it will sometimes cause the seat to have an unstable feeling to the occupant.
The Borlinghaus patent solves this problem by having the lift plate torsionally stabilized to prevent the lift plate from aligning itself into an interference relationship with the top plate or other members of the seat adjuster. This is achieved by a fork and tongue, or sliding finger, interlock of the top plate with the lift plate and with an oblong hole in the lift plate to connect with a jack screw. It can also be achieved with an interlock of the rigid link with the lift plate as well as the oblong hole in the lift plate. However, in each instance, the positioning of the Borlinghaus lift plate adds additional manufacturing complexity to an already complex assembly. For example, each lift plate requires two riveting operations to attach the lift plate to the top plate, as well as two riveting operations to attach the rigid link, for a total of six riveting operations for each seat adjuster assembly and twelve for each seat assembly, since each seat assembly includes two seat adjuster assemblies.